The present invention relates to the production of petroleum from a petroleum bearing formation and, in particular where the petroleum bearing formation is in fluid communication with a cavern in a salt bearing formation.
The drilling of a petroleum producing well requires significant investment. As the demand for petroleum continues to increase and exploitable reserves increasingly are found offshore, there is a continuing need for the most efficient drilling and recovery of the petroleum. Further, there has been an emphasis on secondary recovery techniques to increase the amount of petroleum recovered from existing wells.
Underground caverns, such as those created in salt domes, have been used for the storage of hydrocarbons. Also, there has been suggested a combination of the secondary recovery technique of flooding with the use of a cavity below an oil bearing formation to gain advantages over flooding techniques which do not utilize the cavity. Such an approach is illustrated in U.S. Pat. No. 4,016,930. This technique is expensive, as it requires drilling of one or more secondary wells.
Recovery of petroleum from formations located below the surface of bodies of water such as rivers, lakes, and oceans involves many unique problems not encountered in land based exploration and recovery. Currently, offshore wells which would be considered successful wells if they were onshore, are not successful because of their location offshore. One significant difficulty in offshore production is the storage and transportation of the recovered oil. From many offshore locations building a pipeline to deliver the oil to the shore is not economically justifiable. Thus, produced oil must be transported by tanker to shore. A cost associated with offshore production is the cost of maintaining a tanker as a storage vessel on station to receive the petroleum. The rate of oil production from the well determines how long the tanker needs to stay on station. The cost of maintaining a tanker on station increases with each hour the tanker is present. Alternatively, the tanker travels a circuit loading oil from various wells. Additionally, the longer the tanker is present, the greater the risk that it will be exposed to foul weather not conducive to tanker loading operations. Thus, an offshore well that is in the primary production phase having a slow production rate that would be acceptable on land may be too slow to justify offshore tanker operations. For onshore production, the advantages of the invention include minimizing the requirements for surface storage of petroleum, and reduced potential for environmental hazards.
The present invention provides many advantages and features particularly useful in offshore production. Importantly, it has the advantage of making slow producing wells economically viable. The advantages of the present invention are that a single well is needed, a storage cavern is created which is in fluid communication with the well and the oil producing formation. The formed underground storage cavern eliminates the need for expensive surface storage and the risks associated with surface storage, as well as, the more economical employment of tankers offshore. Another advantage of the present invention is that flow rate can be adjusted so as to fill the cavern in a predetermined period of time. This allows for the efficient planning of tanker schedules. It also allows for the tanker to be filled in a minimum possible time. Another advantage of the present invention is that the creep closure rate of the cavern can be minimized.
In one aspect, the present invention relates to a method of forming a storage cavern associated with a petroleum well. A storage cavern is formed by leaching salt from a salt bearing formation. The salt bearing formation may be located, above, below or beside the petroleum bearing formation. A bore hole is drilled into the petroleum bearing formation and the salt bearing formation without extracting oil from the oil bearing formation. The salt bearing formation is then leached to provide a cavern. Once the cavern is formed to the desired size, the petroleum bearing formation is placed in a condition for production of petroleum, for example, by perforating the casing located in the oil bearing formation. The pressure within the cavern is maintained below the pressure of the petroleum bearing formation, thus causing petroleum to flow from the petroleum bearing formation into the cavern.
In another aspect, the present invention relates to a method for the production of petroleum from the petroleum bearing formation, which involves connecting a cavern in a salt formation to a petroleum bearing formation and maintaining the pressure in the cavern at a predetermined pressure to cause a predetermined flow rate of petroleum from the formation into the cavern. Control of the flow rate can be utilized for coordinating the filling of the cavern with the scheduling of tankers to load the oil stored in the cavern.
Another aspect of the invention relates to a method for the production of petroleum from the petroleum bearing formation in which a single bore hole is drilled that connects the surface, the petroleum bearing formation and the salt bearing formation. Thereafter, the salt is leached from the salt bearing formation to form a cavern. The petroleum bearing formation is placed in condition to produce petroleum and the pressure in the cavern is maintained at a predetermined level to cause petroleum to flow into the cavern.
In yet another embodiment, the present invention relates to a system for producing oil. The system has a wellbore having an opening and which connects a petroleum bearing formation and a cavern. A check valve is placed within a passageway between the petroleum bearing formation and the cavern to allow oil to flow from the petroleum bearing formation into the cavern and prevent flow from the cavem to the petroleum bearing formation. A wellhead tree is provided proximate to the wellbore opening to seal off the wellbore while providing access for the passage of conduits through the wellhead tree. The system includes a displacement conduit for the injection or removal of displacement fluid, such as compressed air, nitrogen or water, into the cavern. A production conduit is also provided which passes through the wellhead tree and extends into the cavern for the removal of petroleum from the well. One or more valves can be located in the conduits to open and close the passageways.